Do you mean the plastic/rough looking surface side? I don’t know. Perhaps someone who uses it can tell us what it’s good for.
I print PLA and TPU on glass with the glue stick and get consistent results… With TPU, I find that just wiping the glass down with an alcohol wipe in between prints and leaving the glue residue is enough for raftless prints that stick every time. Never had an issue. That’s with the TPU head though, which comes with the 300. The PLA head is OK too, and I find I just need enough glue on the glass for a reliable stick.
I do recalibrate for height frequently though, and when I did have a problem it was related to calibration variation, so I followed the instructional video on adjusting the platform through the knobs and it worked great. Variation in platform height does affect stickiness for me.
But I never tried the rough surface… I just use the perfboard plate for ABS. I do get lifting at the corner if it’s not set right, but rarely does anything come unstuck unless I have the platform height set incorrectly.